This invention relates a method and a device for converting the resolution of picture signal as well as converting interlace system picture signal into non-interlace system picture signal, which are applicable to displays, such as plasma display and LC (liquid crystal) display, to display pictures in non-interlace system.
In general, a frame in NTSC television broadcasting is composed of 525 scanning lines (or lines). Moving image is created by sending 30 frames per 1 second. However, in case of 30 frames per 1 second, it is likely to sense some flicker. So, to reduce the flicker in displaying moving image, the interlace system is used.
The interlace system which is one of image displaying systems means xe2x80x9cinterlaced scanningxe2x80x9d. In the interlace system, the scanning from top to bottom is conducted every other line. Thus, by finishing one frame in half time, the flicker is reduced. A complete picture (frame) is created using two frames (fields) each of which is composed of 262.5 scanning lines.
On the other hand, with plasma display or LC display, when displaying in the interlace system, all the more flicker occurs and the brightness lowers. Because of this, the non-interlace system (also called progressive system) which is xe2x80x9csequential scanningxe2x80x9d is used. So, in plasma displays or LC displays, interlace system picture signal needs to be converted into non-interlace system picture signal.
Although picture signal with 525 scanning lines is obtained by converting interlace system picture signal of 262.5 scanning lines into non-interlace system picture signal, plasma displays may be used to display at a resolution with more than (or less than) 525 scanning lines. In such a case, the resolution of picture signal also needs to be converted.
FIG. 1 is a block diagram showing the composition of a conventional resolution conversion device applicable to such a case. In FIG. 1, a two-dimensional scanline interpolation circuit 1 interpolates (estimates a value to be laid between different values from the whole tendency) intermediate picture signal (picture signals between scanning lines) based on picture signal of 262.5 scanning lines, inserting 262.5 interpolation scanning lines into the intervals of 262.5 scanning lines in one field. Thereby, interlace system picture signal of 262.5 scanning lines is converted into non-interlace system picture signal of 525 scanning lines.
A three-dimensional scanline interpolation circuit 2 interpolates picture signal based on picture signal of 262.5 scanning lines in the previous field (or the previous and following fields), inserting 262.5 interpolation scanning lines into the intervals of 262.5 scanning lines in the current field. Thereby, interlace system picture signal of 262.5 scanning lines is converted into noninterlace system picture signal of 525 scanning lines.
A movement detection circuit 3 stores picture signal into frame memory, detecting the difference between previous-frame picture signal and current-frame picture signal, thereby detecting the degree of movement in moving image. A coefficient generator circuit 4 determines a degree of movement in moving image based on difference signal output from the movement detection circuit 3, generating coefficients xcex1, xcex2 according to the degree of movement.
A coefficient multiplier 5 multiplies non-interlace system picture signal output from the two-dimensional scanline interpolation circuit 1 by coefficient xcex2 (=1xe2x88x92xcex1) output from the coefficient generator circuit 4. A coefficient multiplier 6 multiplies non-interlace system picture signal output from the three-dimensional scanline interpolation circuit 2 by coefficient xcex1 (0xe2x89xa6xcex1xe2x89xa61) output from the coefficient generator circuit 4. An adder 7 adds picture signals output from the coefficient multipliers 5 and 6.
A resolution converter circuit 8 converts non-interlace system picture signal of 525 scanning lines output from the adder 7 into picture signal at a given resolution (e.g., of 768 scanning lines). As the resolution conversion method, linear interpolation to weight, based on the position of scanning line to be interpolated and the distance of scanning line in the current field, a reciprocal number of the distance is used. Also, besides the linear interpolation, curve interpolation to weight using a spline function (curve) can be used.
Also, the resolution converter circuit 8 may conduct the conversion of resolution in the horizontal direction (for dots), other than the conversion of resolution in the vertical direction (for scanning line number).
In operation, interlace system picture signal is, as shown in FIG. 1, input to the two-dimensional scanline interpolation circuit 1, three-dimensional scanline interpolation circuit 2 and movement detection circuit 3.
For interlace system picture signal of 262.5 scanning lines, the two-dimensional scanline interpolation circuit 1 interpolates picture signal between scanning lines based on the picture signal of 262.5 scanning lines laid every other line in one field, inserting 262.5 interpolation scanning lines into the intervals of 262.5 scanning lines in one field. Thereby, the interlace system picture signal is converted into non-interlace system picture signal of 525 scanning lines.
Also, for interlace system picture signal of 262.5 scanning lines, the three-dimensional scanline interpolation circuit 2 interpolates picture signal based on the picture signal of 262.5 scanning lines in the previous field (or the previous and following fields), inserting 262.5 interpolation scanning lines into the intervals of 262.5 scanning lines in the current field. Thereby, the interlace system picture signal is converted into non-interlace system picture signal of 525 scanning lines.
For interlace system picture signal of 262.5 scanning lines, the movement detection circuit 3 detects the difference between the previous-frame picture signal and the current-frame picture signal, then outputting it to the coefficient generator circuit 4. The coefficient generator circuit 4 determines a degree of movement in moving image based on the difference signal output from the movement detection circuit 3, outputting coefficients xcex1, xcex2, according to the degree of movement, to the coefficient multipliers 5 and 6.
Coefficients xcex1, xcex2 generated by the coefficient generator circuit 4 are in relations of xcex2=1xe2x88x92xcex1 and 0xe2x89xa6xcex1xe2x89xa61. As coefficient xcex1 increases, coefficient xcex2 decreases. On the contrary, as coefficient xcex2 increases, coefficient xcex1 decreases. Here, when degree of movement is low, the coefficient generator circuit 4 increases coefficient xcex1 to increment the influence of picture signal (static image) output from the three-dimensional scanline interpolation circuit 2. When degree of movement is high, the coefficient generator circuit 4 increases coefficient xcex2 to increment the influence of picture signal (dynamic image) output from the two-dimensional scanline interpolation circuit 1. Such signal processing based on the degree of movement in moving image is called movement-adaptive signal processing.
Non-interlace system picture signal (of 525 scanning lines) output from the two-dimensional scanline interpolation circuit 1 is multiplied by coefficient xcex2 by the coefficient multiplier 5, then output to the adder 7. Also, non-interlace system picture signal (of 525 scanning lines) output from the three-dimensional scanline interpolation circuit 2 is multiplied by coefficient xcex1 by the coefficient multiplier 6, then output to the adder 7. The two non-interlace system picture signals (of 525 scanning lines) are added by the adder 7, then output to the resolution converter circuit 8.
Then, in case of linear interpolation, the resolution converter circuit xcex1 interpolates the noninterlace system picture signal (of 525 scanning lines) to weight, based on the position of scanning line to be interpolated and the distance of scanning line in the current field, a reciprocal number of the distance. Thereby, it is converted into picture signal at a given resolution (e.g., of 768 scanning lines), then output. Meanwhile, as the case may be, the number of dots (number of pixels) in the scanning line is also converted.
Thus, in the conventional resolution conversion device above-mentioned, interlace system picture signal (of 262.5 scanning lines) is converted into non-interlace system picture signal (of 525 scanning lines) by the first-stage two-dimensional scanline interpolation circuit 1 and three-dimensional scanline interpolation circuit 2. Then, the non-interlace system picture signal (of 525 scanning lines) is converted into non-interlace system picture signal at a given resolution (e.g., of 768 scanning lines) by the second-stage resolution converter circuit 8. So, there is a problem that the quality of image deteriorates by the two-stage conversion processing.
Namely, in generally, filtering in digital signal processing causes an error by the cut-off processing of data. Therefore, in case of two-stage conversion processing in the conventional resolution conversion device above, error accumulates by that much, thereby causing a deterioration in image. Also, when using the linear interpolation for the interpolation processing during the two-stage conversion processing, error can be reduced by assigning equal coefficients (e.g., weighting of a parameter such as a position of scanning line and a distance of scanning line) for the two interpolation processes, even when the interpolation is conducted at two stages. However, when using the curve interpolation, due to a difference in conversion ratio, it is difficult to assign equal coefficients for the two interpolation processes. So, error increases, so that the quality of image can deteriorate.
Accordingly, it is an object of the invention to provide a resolution conversion method that high-quality images can be yielded while suppressing deterioration in image.
It is a further object of the invention to provide a resolution conversion device that high-quality images can be yielded while suppressing deterioration in image.
According to the invention, a method for converting interlace system picture signal into non-interlace system picture signal, comprises the step of:
conducting the interpolation of scanning line while varying coefficient to weight scanning lines of interlace system picture signal to each of interpolation scanning lines to be inserted into the interval of the scanning lines of interlace system picture signal and simultaneously varying the coefficient to weight scanning lines of interlace system picture signal to each of fields.
According to another aspect of the invention, a device for converting interlace system picture signal into non-interlace system picture signal, comprises:
scanline interpolation and resolution conversion circuit for conducting the interpolation of scanning line at a given resolution while varying coefficient to weight scanning lines of interlace system picture signal to each of interpolation scanning lines to be inserted into the interval of the scanning lines of interlace system picture signal and simultaneously varying the coefficient to weight scanning lines of interlace system picture signal to each of fields.
According to another aspect of the invention, a device for converting interlace system picture signal into non-interlace system picture signal, comprises:
a two-dimensional scanline interpolation and resolution conversion circuit for converting interlace system picture signal into non-interlace system picture signal based on picture signal of scanning lines in one field;
a three-dimensional scanline interpolation and resolution conversion circuit for converting interlace system picture signal into non-interlace system picture signal based on picture signal of scanning lines in previous field or multiple fields; and
a movement-adaptive processing circuit for detecting the difference between previous-frame picture signal and current-frame picture signal, detecting degree of movement in image by converting the resolution of the difference signal, and varying the ratio of addition to the picture signals output from the two-dimensional scanline interpolation and resolution conversion circuit and the three-dimensional scanline interpolation and resolution conversion circuit according to the degree of movement;
wherein the two-dimensional scanline interpolation and resolution conversion circuit and the three-dimensional scanline interpolation and resolution conversion circuit conduct the interpolation of scanning line at a given resolution while varying coefficient to weight scanning lines of interlace system picture signal to each of interpolation scanning lines to be inserted into the interval of the scanning lines of interlace system picture signal and simultaneously varying the coefficient to weight scanning lines of interlace system picture signal to each of fields.
According to another aspect of the invention, a method for converting interlace system picture signal into non-interlace system picture signal, comprises the step of:
converting the interlace system picture signal into non-interlace system picture signal at a given resolution by one conversion process.
According to another aspect of the invention, a device for converting interlace system picture signal into non-interlace system picture signal, comprises:
circuit for converting the interlace system picture signal into non-interlace system picture signal at a given resolution by one conversion process.